1. Field of The Invention
This invention relates to a device for detecting a recording/reproducing element.
2. Description of The Related Art
As an example of a typical magnetic recording/reproducing apparatus adapted to record on and reproduce from a magnetic tape an information signal by using magnetic rotating heads (hereunder sometimes referred to simply as a rotating heads), a video tape recorder (VTR) can be cited. Further, it is well known that rapid progress to date has provided current VTRs with excellent picture quality and advanced functions. Moreover, earnest work is now in progress to develop a digital VTR which is used to record digital signals.
Further, the VTR of the above described type (namely, the VTR adapted to record on and reproduce from a magnetic tape an information signal by using rotating heads) is generally used to record continuous images such as a television broadcast programme and a video picture taken by using a television camera. Recently, in view of the fact that a magnetic tape used in a VTR has large storage capacity, it has come to make an attempt to use a VTR as a composing member (for example, a storage device) of a digital information processing system.
Furthermore, in case where such a VTR is used as a composing member of a digital information processing system, for example, an external auxiliary storage device for a computer system or as a device for sequentially recording images produced by using computer graphics techniques upon completion of calculation of data representing the images and for generating an animation by continuously reproducing the recorded images, the recording of information signals is sometimes performed in such a manner that the information signals is recorded on a magnetic tape in track units or in several tracks. Therefore, for the purpose of employing such a VTR as a composing member of an information processing system, it is necessary to achieve an operation of recording information on a magnetic tape, for instance, in track units or in several tracks in a highly stable and reliable manner.
In case that an information signal is recorded on a specific track in a magnetic tape or the contents of a record on a specific track in the magnetic tape are modified in a VTR of the type in which records on and reproduces from the magnetic tape an information signal by using rotating heads, the following conventional methods for recording the information signal on the magnetic tape are performed. Namely, in case of performing a first conventional method, the magnetic tape is preliminarily rewound by effecting a pre-rolling operation in such a manner that a position prior to a predetermined starting position, from which the recording of an information signal should be started, on the magnetic tape is adjusted to the rotating head. When starting the recording of the information signal, the magnetic tape is rapidly moved forward therefrom, so that the starting position on the magnetic tape passes through the rotating head at a predetermined tape transporting speed and thus the information signal is recorded on a predetermined number of tracks from the starting position on the magnetic tape. In contrast, in case of performing a second conventional method, a portion, on which an information signal should be recorded, of a magnetic tape is first stopped at a place, at which the recording of the information signal is performed, of a VTR by using a control pulse and controlling the position of a capstan motor. Then, the information signal is recorded by using a rotating head on the portion of the magnetic tape which is at a standstill.
The above described first conventional method is performed in what is called an assembly recording mode (i.e., in an electronic splicing mode) and in what is called an insert-type recording mode (i.e., in an insert-type electronic editing mode) of an electronic editing of a record in a conventional VTR. This method, however, is not suited for a case in which the above described recording operation is frequently performed. This is because the first conventional method requires the repetition of steps of rewinding a magnetic tape and transporting the tape forward every time an information signal is recorded on a magnetic tape so as to charge a large burden against and waste a tape transport mechanism of the VTR and the magnetic tape. Moreover, the conventional VTR has another drawback that it is difficult to set the position of a track with high precision because of the fact that the position of a track on which an information signal should be recorded is determined by a relative motion of a rotating head of the VTR with respect to the magnetic tape which is running. Furthermore, the conventional VTR has still another drawback that the pre-rolling operation takes time and thus a time interval between two consecutive recording operations cannot be decreased to a desirable extent.
In contrast, the above described second conventional method does not require the rewinding operation as required in the first conventional method. Further, in case of employing the second conventional method, a recording operation is performed while a magnetic tape is at a standstill. Thus the second conventional method has advantages that there is no case in which a large burden is charged against the tape transport mechanism and the magnetic tape and that the position of a track can be easily set with high precision. However, as described above, an information signal is recorded by using a rotating head on a magnetic tape which is stationary. This results in that the pattern of records formed in a track on a magnetic tape by effecting the second conventional method becomes different from that of records formed in a track on a magnetic tape, which runs at a predetermined speed, correspondingly to the locus of the rotation of a magnetic rotating head. Therefore, when the information represented by the information signal recorded on the magnetic tape by performing the second conventional method is reproduced in a state in which the magnetic tape is running at a predetermined running speed, the track cannot be exactly tracked by the rotating head. Further, it is difficult to record information on tracks, a part of which are formed on a magnetic tape by effecting the second conventional method and mixed with the other tracks formed on the same magnetic tape moving at a predetermined running speed, and to use the recorded information.
For the purpose of eliminating the drawbacks of the first and second conventional methods, has been proposed a VTR provided with an actuator for controlling the locus of the rotation of a magnetic rotating head at the time of intermittently performing recording operations on the basis of a position signal generated correspondingly to an absolute position of the rotating head, which is measured by using a reference edge of the magnetic tape as a reference position, in such a manner that a record of an information signal similar to, for example, another record thereof formed on the magnetic tape, which moves at a predetermined running speed in a predetermined direction, correspondingly to the locus of the rotation of the rotating head is formed according to the locus of the rotating head with respect to the magnetic tape which stops after intermittently moves by a predetermined distance at a time in the running direction.
Further, a VTR provided with such an actuator needs to stably detect the exact position of the rotating head. For example, Japanese Patent Application Provisional Publication No. 52-117105 discloses a VTR (hereunder sometimes referred to as a first conventional VTR) having such an actuator composed of an electro-mechanical transducing element formed by using an electrostrictive material, which is adapted to detect the displacement of the actuator by employing a strain gauge adhering to the electro-mechanical transducing element formed from the electrostrictive material.
Although the first conventional VTR can suppress the free oscillation of the actuator by first generating a speed signal representing the speed of the actuator by differentiating the displacement of the actuator and then feeding back the speed signal to a drive circuit, the first conventional VTR cannot detect the position of the rotating head.
This is because a VTR adapted to detect a quantity of an warp or distortion of an electrostrictive material composing an electro-mechanical transducing element like the first conventional VTR cannot detect the position of a rotating head on the basis of the detected quantity of the warp of the electrostrictive material owing to the facts that the quantity of the warp or distortion of the electrostrictive material indicates a hysteresis characteristic and that the state of the warp of the electrostrictive changes according to temperature.
The present invention is created to eliminate the drawbacks of the conventional VTRs.
It is, therefore, a first object of the present invention to provide a device for detecting the position of a recording/reproducing element of a VTR, which can improve the precision of the detection of the recording/reproducing element and completely eliminate a drift at the stationary position of the recording/reproducing element and obtain a position detecting signal having a preferable signal-to-noise ratio (S/N).
Referring to FIGS. 18(a) and 18(b), there is illustrated a conventional drive device for driving a magnetic head 117 of a VTR which drives and displaces the magnetic head 117 by using a voice coil motor and detects the position of the magnetic head by displacing a light shielding member 118 mounted at a moving portion of the drive device on an optical path from a light emitting diode 119 to a photodiode 120. In FIG. 18(a), reference numeral 113 designates a base portion; and 114 a sensor fixing stand. As shown in this figure, a magnetic-head holding member 115 is rigidly connected to an elastic supporting portion 116 fixed on the base portion 113. Moreover, the magnetic head 117 is mounted on an edge portion of the magnetic-head holding member 115. Furthermore, the light shielding member 118 is fixed on the top surface of the magnetic-head holding member 115, and a moving coil 124 is fixed on the bottom surface of the member 115.
The moving coil 124 fixed on the bottom surface of the magnetic-head holding member 115 is placed in a space formed among the inner surface of a cylindrical yoke 121 having a bottom, which is fixed on the base portion 113, and the outer surfaces of a permanent magnet 122 and a center pole 123 which are fixed on the yoke 121 in such a manner that the yoke 121, the magnet 122 and the pole 123 are coaxial. When supplying electric current to the moving coil 124, the magnetic-head holding member 115 is upwardly and downwardly driven and displaced, as viewed in FIG. 18, by an electromagnetic force generated due to both of an electric current flowing through the moving coil 124 and a magnetic flux produced in the space formed among the yoke 121, the magnet 122 and the pole 123. Consequently, the magnetic head 117 and the light shielding member 118 fixed on the magnetic-head holding portion 115 are also upwardly and downwardly driven and displaced, as viewed in FIG. 18.
Further, the light shielding member 118 fixed on the magnetic-head holding member 115 is inserted in the optical path between the light emitting diode 119 and the photodiode 120 mounted on the sensor fixing stand 114. Thus an output signal of the photodiode 120 changes correspondingly to the position of the light shielding member 18, the change of which is similarly to that of the position of the magnetic head 117 fixed on the magnetic-head holding member 115. Consequently, the position of the magnetic head 117 can be detected on tile basis of the output signal of the photodiode 120.
However, in case of the conventional device of FIG. 18, when a mounting member fixed on the sensor fixing stand 114 for mounting the light emitting diode 119 and the photodiode 120 (namely, a case for fixing and protecting the light emitting diode 119 and the photodiode 120) contracts in the direction indicated by an arrow Z of FIG. 18(b) owing to change in environmental temperature, the position of the light shielding member 118 inserted in the optical path from the light emitting diode 119 to the photodiode 120 relatively changes with respect to the diode 119 or the photodiode 120. This causes an error in the result of the detection of the position of the magnetic head 117.
Further, in a reproducing mode, it matters little in an operation of a closed-loop tracking control whether an error occurs in the result of the detection of the magnetic head 117. In contrast with this, in a recording mode, an error occurring in the result of the detection of the position of the magnetic head 117 gets into serious trouble. The reason is as follows. Namely, the mounting member fixed on the sensor fixing stand 114 for mounting the light emitting diode 119 and the photodiode 120 (namely, the case for fixing and protecting the light emitting diode 119 and the photodiode 120) is usually made of synthetic resin having a large coefficient of thermal expansion. Thus, the magnitude of an error occurring in the result of the detection of the position of the magnetic head 117 owing to change in environmental temperature cannot be ignored. Consequently, in case of a magnetic recording/reproducing apparatus which performs a recording operation by detecting the position of the magnetic head in a recording mode, an error occurring in the result of the detection of the position of the magnetic head 117 gets into serious trouble as above stated. Further, a means of settling the trouble is demanded.
It is, accordingly, a second object of the present invention to provide a device for detecting the position of a recording/reproducing element, which does not generate an error in the result of the detection of the position of the recording/reproducing element even when environmental temperature changes.